1. Field of the Invention
The invention relates to a constant velocity universal joint for use in power transmission devices in motor vehicles and various industrial machines. In particular, the invention relates to a tripod type constant velocity universal joint.
2. Description of the Related Art
Tripod type constant velocity universal joints are used, for example, as an element in a power transmission device for transmitting rotational power from a car engine to wheels.
In general, a tripod type constant velocity universal joint is chiefly composed of an outer joint member and a tripod member. The outer joint member has an inner periphery provided with three axially-extending track grooves. Each of the track grooves has axial roller guideways on both sides. The tripod member is provided with three radially-projecting trunnions. A roller is rotatably arranged on each of the trunnions. The trunnions of the tripod member and the roller guideways of the outer joint member engage with each other in the direction of rotation via the rollers so that rotational torque is transmitted from a drive side to a driven side at constant velocity. The individual rollers rotate about the trunnions and roll on the roller guideways as well, absorbing relative axial displacements and angular displacements between the outer joint member and the tripod member. In the meantime, also absorbed are axial displacements of the individual trunnions to the roller guideways, the axial displacements resulting from phase changes in the direction of rotation when the outer joint member and the tripod member transmit rotational torque with some operating angle therebetween.
Some tripod type constant velocity universal joints have the rollers mounted on cylindrical outer peripheries of their trunnions via a plurality of needle rollers. When an outer joint member and a tripod member transmit rotational torque with an operating angle, however, the trunnions tilt to make the rollers and the respective roller guideways oblique to each other. This produces a slide therebetween, giving rise to a problem that resistance here hampers the smooth rolling of the rollers and thereby increases induced thrust. Moreover, there is another problem that the resistance between the rollers and the respective roller guideways increases the slide resistance to axial relative displacements between the outer joint member and the tripod member. Such induced thrust and slide resistance contribute to the production of vibrations and noises from a car body, affecting the Noise Vibration Harshness (hereinafter referred to as “NVH”) performances of the motor vehicle. Typical automotive NVH phenomena associated with such induced thrust and slide resistance include the rolling of a moving car body and the vibrations of a car idling with its automatic transmission in the drive or D range, respectively. The essence of solution to the automotive NVH problems consists in reducing the induced thrust and slide resistance in the joint. In general, induced thrusts and slide resistances in a joint tend to depend on operating angle of the joint. This tendency leads to a design limitation of prohibiting greater operating angles when, for example, a constant velocity universal joint is applied to an automotive drive shaft. Accordingly, reduction and stabilization of the induced thrust and slide resistance are also desired for the sake of enhanced design flexibility of portions around the car axles.
Conventionally, to eliminate the oblique states between the rollers and the roller guideways to lower the induced thrust and slide resistance, there have been proposed and put into practical use a variety of tripod type constant velocity universal joints that comprise mechanisms (roller assemblies) for allowing tilting movements of the rollers with respect to the trunnions. Among the known tripod type constant velocity universal joints of this kind is a constitution comprising outer rollers to be guided by the roller guideways and inner rollers rotatably supported by the outer peripheries of the trunnions via a plurality of needle rollers. This constitution is then broadly divided into the following modes a) to d).
a) The outer rollers are provided with outer peripheries of convex spherical shape (including both a “perfect spherical surface,” having its center of curvature on the trunnion axis, and a so-called “torus surface,” having its center of curvature off the trunnion axis toward the outer-diameter side) and inner peripheries of cylindrical shape, and the inner rollers are provided with outer peripheries of convex spherical shape, so that slides between the cylindrical inner peripheries of the outer rollers and the convex-spherical outer peripheries of the inner rollers permit the tilting movements of the outer rollers.
b) The outer rollers are provided with outer peripheries of convex spherical shape (including both a perfect spherical surface and a torus surface) and inner peripheries shaped so as to make line contact with outer peripheries of the inner rollers, and the inner rollers are provided with the outer peripheries of convex spherical shape, so that slides between the inner peripheries of the outer rollers and the convex-spherical outer peripheries of the inner rollers permit the tilting movements of the outer rollers. Besides, the inner peripheries of the outer rollers are shaped so that load components toward the trunnion extremities are created at the contact positions with the outer peripheries of the inner rollers.
c) The roller guideways are provided with flat surfaces, the outer rollers are with outer peripheries of cylindrical shape and inner peripheries of concave spherical shape, and the inner rollers are with outer peripheries of convex spherical shape, so that slides between the concave-spherical inner peripheries of the outer rollers and the convex-spherical outer peripheries of the inner rollers permit the tilting movements of the outer rollers.
d) In addition to the constitution c) above, the roller guideways and the axes of the trunnions are configured not to be parallel to each other at an operating angle of 0°.
Also known as a tripod type constant velocity universal joint of this kind is the constitution e) in which: the outer peripheries of the trunnions are shaped into a convex spherical surface (a perfect spherical surface having the center of curvature on the trunnion axis); the rollers are mounted onto support rings via a plurality of needle rollers to constitute roller assemblies; and cylindrical inner peripheries of the support rings are fitted to the convex-spherical outer peripheries of the trunnions. The plurality of needle rollers are arranged without any retainers, or in a so-called full complement state. According to this constitution, slides between the cylindrical inner peripheries of the support rings and the convex-spherical outer peripheries of the trunnions allow the tilting movements of the roller assemblies including the rollers.
In constant velocity universal joints comprising roller assemblies of this type, axial relative movements of the rollers and the support rings are restricted from both sides by engaging means so that the roller assemblies are secured in their unity as assembled articles. On the other hand, when a constant velocity universal joint of this kind transmits rotational torque at an operating angle, tilting movements and axial movements of the roller assemblies with respect to the trunnions produce slides between the inner peripheries of the support rings and the outer peripheries of the trunnions. Then, the sliding frictional forces therein cause axial repetitive loads (hereinafter, simply referred to as “axial loads”) onto the engaging means, along the axial directions of the rollers and the support rings. Hence, the engaging means require such strengths as to stand the axial loads (strengths against bending fatigue, cracking fatigue, and the like). Besides, the engaging means make sliding contact with the end faces of the rollers and/or the support rings and, in the cases where the rollers are rotatably supported by the support rings via needle rollers, even with the end faces of the needle rollers. This brings about another problem of the fatigue life of those contact surfaces.